Scheme simplifies quantum chips

December 15/22, 2004

Quantum computers promise to solve certain
types of very large problems many orders of magnitude faster than today's
computers, but coaxing quantum particles like atoms, photons and electrons
to carry out computations is no small matter.

Researchers from the University of California at Berkeley and
the University of Maryland have brought practical quantum computers a
step closer by proposing a type of quantum bit that is relatively easy
to build. Qubit's, like ordinary computer bits, represent the 1s and 0s
of computer information.

The researchers' architecture sidesteps the previous requirement
of extreme precision in the placement of spin qubits -- a tiny area of
semiconductor that traps a particle that can represent a 1 or a 0 depending
on its spin direction. Spin direction can be pictured as the two possible
ways to spin a top -- clockwise or counterclockwise.

The architecture uses electron spin rather than atomic spin, which
is more difficult to measure. The qubits in the researchers' scheme are
connected through the magnetic interaction between atoms rather than the
influence closely positioned electrons have on each other. Ordinarily
magnetic interaction would cause every qubit to be permanently connected
to every other qubit.

The researchers devised a method to connected and disconnect such
qubits. The method allows qubits to be placed further apart than those
of previous quantum architectures. This, in turn, allows them to be positioned
by ion implantation, an easy-to-use technique that calls for shooting
them into the silicon chip with a gun-like device.

It will take at least ten years to build a useful quantum computer
device with only a few working qubits, according to the researchers. Many
researchers agree that practical quantum computers are two decades away.
The work appeared in the November 5, 2004 issue of Physical Review
A.